/*-------------------------------------------------------------------------
*
* Copyright (c) 2004-2005, PostgreSQL Global Development Group
* Copyright (c) 2004, Open Cloud Limited.
*
* IDENTIFICATION
*   $PostgreSQL: pgjdbc/org/postgresforest/core/Query.java,v 1.4 2005/01/11 08:25:43 jurka Exp $
*
*-------------------------------------------------------------------------
*/
package org.postgresforest.core;

/**
 * Abstraction of a generic Query, hiding the details of
 * any protocol-version-specific data needed to execute
 * the query efficiently.
 *<p>
 * Query objects should be explicitly closed when no longer
 * needed; if resources are allocated on the server for this
 * query, their cleanup is triggered by closing the Query.
 *
 * @author Oliver Jowett (oliver@opencloud.com)
 */
public interface Query {
    /**
     * Create a ParameterList suitable for storing parameters
     * associated with this Query.
     *<p>
     * If this query has no parameters, a ParameterList will
     * be returned, but it may be a shared immutable object.
     * If this query does have parameters, the returned
     * ParameterList is a new list, unshared by other callers.
     *
     * @return a suitable ParameterList instance for this query
     */
    ParameterList createParameterList();

    /**
     * Stringize this query to a human-readable form, substituting
     * particular parameter values for parameter placeholders.
     *
     * @param parameters a ParameterList returned by this Query's
     *  {@link #createParameterList} method, or <code>null</code> to
     *  leave the parameter placeholders unsubstituted.
     * @return a human-readable representation of this query
     */
    String toString(ParameterList parameters);

    /**
     * Close this query and free any server-side resources associated
     * with it. The resources may not be immediately deallocated, but
     * closing a Query may make the deallocation more prompt.
     *<p>
     * A closed Query should not be executed.
     */
    void close();
}
